Urethral Evoked Sympathetic Skin Responses and Viscerosensory Evoked Potentials as Diagnostic Tools to Evaluate Urogenital Autonomic Afferent Innervation in Spinal Cord Injured Patients

Abstract

In most spinal cord injured (SCI) patients the objective assessment of afferent neuronal pathways from the lower urinary tract and the recording of a disturbed urethral sensation and/or desire to void are still difficult. Viscerosensory evoked potentials (VSEPs) might be helpful, but they remain technically difficult to obtain and interpretation is delicate. As a new approach, sympathetic skin response (SSR) of the hand and foot were recorded after electrical stimulation of the posterior urethral mucosa. This technique should allow assessment of the integrity or deterioration of the autonomic afferent pathway. A total of 20 males and 8 females with SCI somatosensory incomplete 15, somatosensory complete 13 and 6 healthy male volunteers were prospectively examined. During urodynamic examination electrical stimulation (single square pulses of 0.2 ms, 2 to 3-fold sensory threshold, 60 mA in complete SCI patients) of the posterior urethra/bladder neck was performed using a bipolar electrode inserted into a microtip pressure catheter. SSR recordings of the right palm and sole were simultaneously taken using surface electrodes and were analyzed by an electromyography unit. Patient reports on evoked urethral sensations at individual sensory thresholds were simultaneously noted. Additionally, well-known electrophysiological measurements such as pudendal sensory evoked potential and urethral VSEP were recorded to check clinical assessed somatosensory and viscerosensory status, and to compare SSR results with these conventional methods. Electrical stimulation of the posterior urethra evoked clear urethral sensation and SSRs in normal subjects. In 14 of 15 sensory incomplete SCI patients with disturbed urethral sensation SSRs could be recorded as well. Electrically evoked urethral sensations resembled the subjective desire to void at full bladder reported by controls and patients. In 13 sensory complete SCI patients with loss of any urethral sensation SSRs could not be recorded even at maximal electrical stimulation strength. All subjects with electrically induced urethral sensation had positive evoked (supralesional) SSRs of the hand. However, none of the patients with absent urethral sensation presented SSRs. Simultaneously recorded VSEPs could not be recorded clearly in 5 patients and 2 control subjects, whereas SSRs delivered clear results in all controls and patients, matching their reports. SSR recordings above a spinal lesion level after urethral electrostimulation might provide a useful and technically simple objective diagnostic tool to assess integrity of autonomic (visceral) afferent nerves from the lower urinary tract. Somatosensory deficits are not always paralleled by viscerosensory loss and vice versa. In this study SSRs were superior to VSEPs, the latter being more difficult to record. The subjective sensations reported by subjects during stimulation could be confirmed in an objective way in 100% of cases by positive/negative SSR findings.